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1.
Summary. Glutathione (reduced form GSH and oxidized form GSSG) constitutes an important defense against oxidative stress in the brain,
and taurine is an inhibitory neuromodulator particularly in the developing brain. The effects of GSH and GSSG and glycylglycine,
γ-glutamylcysteine, cysteinylglycine, glycine and cysteine on the release of [3H]taurine evoked by K+-depolarization or the ionotropic glutamate receptor agonists glutamate, kainate, 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate
(AMPA) and N-methyl-D-aspartate (NMDA) were now studied in slices from the hippocampi from 7-day-old mouse pups in a perfusion system.
All stimulatory agents (50 mM K+, 1 mM glutamate, 0.1 mM kainate, 0.1 mM AMPA and 0.1 mM NMDA) evoked taurine release in a receptor-mediated manner. Both
GSH and GSSG significantly inhibited the release evoked by 50 mM K+. The release induced by AMPA and glutamate was also inhibited, while the kainate-evoked release was significantly activated
by both GSH and GSSG. The NMDA-evoked release proved the most sensitive to modulation: L-Cysteine and glycine enhanced the
release in a concentration-dependent manner, whereas GSH and GSSG were inhibitory at low (0.1 mM) but not at higher (1 or
10 mM) concentrations. The release evoked by 0.1 mM AMPA was inhibited by γ-glutamylcysteine and cysteinylglycine, whereas
glycylglycine had no effect. The 0.1 mM NMDA-evoked release was inhibited by glycylglycine and γ-glutamylcysteine. In turn,
cysteinylglycine inhibited the NMDA-evoked release at 0.1 mM, but was inactive at 1 mM. Glutathione exhibited both enhancing
and attenuating effects on taurine release, depending on the glutathione concentration and on the agonist used. Both glutathione
and taurine act as endogenous neuroprotective effectors during early postnatal life.
Authors’ address: Prof. Simo S. Oja, Brain Research Center, Medical School, FI-33014 University of Tampere, Finland 相似文献
2.
Nitrate reductase (NR) activity in spinach leaf extracts prepared in the presence of a protein phosphatase inhibitor (50 μM
cantharidine) was measured in the presence of Mg2+ (NRact) or EDTA (NRmax), under substrate saturation. These in-vitro activities were compared with nitrate reduction rates
in leaves from nitrate-sufficient plants. Spinach leaves containing up to 60 μmol nitrate per g fresh weight were illuminated
in air with their petiole in water. Their nitrate content decreased with time, permitting an estimation of nitrate reduction
in situ. The initial rates (1–2 h) of nitrate consumption were usually lower than NRact, and with longer illumination time
(4 h) the discrepancy grew even larger. When leaves were fed through their petiole with 30 mM nitrate, initial in-situ reduction
rates calculated from nitrate uptake and consumption were still lower than NRact. However, nitrate feeding through the petiole
maintained the in situ-nitrate reduction rate for a longer time. Initial rates of nitrate reduction in situ only matched NRact
when leaves were illuminated in 5% CO2. In CO2-free air or in the dark, both NRact and in-situ nitrate reduction decreased, but NRact still exceeded in-situ reduction.
More extremely, under anoxia or after feeding 5-amino-4-imidazole carboxyamide ribonucleoside in the dark, NR was activated
to the high light level; yet in spite of that, nitrate reduction in the leaf remained very low. It was examined whether the
standard assay for NRact would overestimate the in-situ rates due to a dissociation of the inactive phospho-NR-14-3-3 complex
after extraction and dilution, but no evidence for that was found. In-situ NR obviously operates below substrate saturation,
except in the light at high ambient CO2. It is suggested that in the short term (2 h), nitrate reduction in situ is mainly limited by cytosolic NADH, and cytosolic
nitrate becomes limiting only after the vacuolar nitrate pool has been partially emptied.
Received: 19 June 1999 / Accepted: 12 October 1999 相似文献
3.
Maize (Zea mays L.) cell cultures incorporated radioactivity from [14C]cinnamate into hydroxycinnamoyl-CoA derivatives and then into polysaccharide-bound feruloyl residues. Within 5–20 min, the
CoA pool had lost its 14C by turnover and little or no further incorporation into polysaccharides then occurred. The system was thus effectively a
pulse–chase experiment. Kinetics of radiolabelling of diferulates (also known as dehydrodiferulates) varied with culture age.
In young (1–3 d) cultures, polysaccharide-bound [14C]feruloyl- and [14C]diferuloyl residues were both detectable within 1 min of [14C]cinnamate feeding. Thus, feruloyl residues were dimerised <1 min after their attachment to polysaccharides. For at least
the first 2.3 h after [14C]cinnamate feeding, polysaccharide-bound [14C]diferuloyl residues remained almost constant at ≈7% of the total polysaccharide-bound [14C]ferulate derivatives. Since feruloyl residues are attached to polysaccharides <1 min after the biosynthesis of the latter,
and >10 min before secretion, the data show that extensive feruloyl coupling occurred intra-protoplasmically. Exogenous H2O2 (1 mM) caused little additional feruloyl coupling; therefore, wall-localised coupling may have been peroxidase-limited. In
older (e.g. 4 d) cultures, less intraprotoplasmic coupling occurred: during the first 2.5 h, polysaccharide-bound [14C]diferuloyl residues were a steady 1.4% of the total polysaccharide-bound [14C]ferulate derivatives. In contrast to the situation in younger cultures, exogenous H2O2 induced a rapid 4- to 6-fold increase in all coupling products, indicating that coupling in the walls was H2O2-limited. In both 2- and 4-d-old cultures, polysaccharide-bound 14C-trimers and larger coupling products exceeded [14C]diferulates 3- to 4-fold, but followed similar kinetics. Thus, although all known dimers of ferulate can now be individually
quantified, it appears to be trimers and larger products that make the major contribution to cross-linking of wall polysaccharides
in cultured maize cells. We argue that feruloyl arabinoxylans that are cross-linked before and after secretion are likely
to loosen and tighten the cell wall, respectively. The consequences for the control of cell expansion and for the response
of cell walls to an oxidative burst are discussed.
Received: 19 January 2000 / Accepted: 13 April 2000 相似文献
4.
Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide composition of the CWM was identical for unfermented
and fermented beans. Polysaccharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na2CO3, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for each fraction was similar for unfermented and fermented
samples, indicating that fermentation caused no significant modification of the structural features of individual cell wall
polysaccharides. Pectic polysaccharides accounted for 60% of the cell wall polysaccharides but only small amounts could be
solubilised in solutions of CDTA, Na2CO3, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characterised by a rhamnogalacturonan
backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the
presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and
a galactoglucomannan accounted for 28%, 8% and 3% of the cell wall polysaccharides, respectively. It is concluded that the
types and structural features of cell wall polysaccharides in cocoa beans resemble those found in the parenchymatous tissue
of many fruits and vegetables rather than those reported for many seed storage polysaccharides.
Received: 29 May 1999 / Accepted: 19 October 1999 相似文献
5.
The dye FM1-43 was used alone or in combination with measurements of the membrane capacitance (Cm) to monitor membrane changes in protoplasts from Viciafaba L. guard cells. Confocal images of protoplasts incubated with FM1-43 (10 μM) at constant ambient osmotic pressure (πo) revealed in confocal images a slow internalisation of FM1-43-labelled membrane into the cytoplasm. As a result of this process
the relative fluorescence intensity of the cell interior (fFM,i) increased with reference to the total fluorescence (fFM,t) by 7.4 × 10−4 min−1. This steady internalisation of dye suggests the occurrence of constitutive endocytosis under constant osmotic pressure.
Steady internalisation of FM1-43 labelled membrane caused a prominent staining of a ring-like structure located beneath the
plasma membrane. Abrupt elevation of πo by 200 mosmol kg−1 caused, over the first minutes of incubation, a rapid internalisation of FM1-43 fluorescence into the cytoplasm concomitant
with a decrease in cell perimeter. Within the first 5 min the cell perimeter decreased by 7.9%. Over the same time fFM,i/fFM,t increased by 0.13, reflecting internalisation of fluorescent label into the cytoplasm. Combined measurements of Cm and total fluorescence of a protoplast (fFM,p) showed that an increase in πo evoked a decrease in Cm but no change in fFM,p. This means that surface contraction of the protoplast is due to retrieval of excess membrane from the plasma membrane and
internalisation into the cytoplasm. Further inspection of confocal images revealed that protoplast shrinking was only occasionally
associated with internalisation of giant vesicles (median diameter 2.7 μm) with FM1-43-labelled membrane. But, in all cases,
osmotic contraction was correlated with a diffuse distribution of FM1-43 label throughout the cytoplasm. From this, we conclude
that endocytosis of small vesicles into the cytoplasm is the obligatory process by which cells accommodate an osmotically
driven decrease in membrane surface area.
Received: 4 May 1999 / Accepted: 19 August 1999 相似文献
6.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
7.
Summary. 3-Hydroxynorvaline (HNV; 2-amino-3-hydroxypentanoic acid), a microbial L-threonine analogue, is toxic to mammalian cells and
displays antiviral properties. In view of this, we investigated the toxicity and/or potential teratogenicity of HNV in developing
chicken and mouse embryos. HNV was administered to chicken embryos (in ovo; dose 75–300 μmole/egg; 48 h post-incubation) and pregnant Hanover NMRI mice (per os; total dose 900–1800 mg/kg body mass; gestation days 7–9). Control animals received sterile saline solutions. Harvested embryos
(chicken embryos, 10 days post-incubation; mouse embryos; gestation day 18) were fixed in glutaraldehyde and stereomicroscopically
inspected for signs of dysmorphogenesis. Body mass, body and toe length and mortality of chicken embryos, and the body mass
and mortality of mouse embryos were recorded. HNV exposure significantly increased the incidence of embryotoxic (growth retardation,
toxic mortality) and congenital defects in both chicken and mouse embryos. All the observed effects were dose-dependent. In
conclusion, HNV is an embryotoxic and teratogenic compound, which caused significant developmental delay and congenital defects
in developing chicken and mouse embryos. 相似文献
8.
Summary. Our observations on the growth stimulatory nature of mimosine, (β-(3-hydroxy-4-pyridon-1-yl)-L-alanine), the toxic non-protein
plant amino acid, in some model experimental systems, warranted sensitive and selective routine estimations. For the determination
of both mimosine and DHP, an indirect spectrophotometric method was developed based on their individual reaction with known
excess of DZSAM and by estimating the remaining DZSAM with N-(1-naphthyl)ethylene-diamine (NEDA). The resultant decrease in
the secondary coupled product was measured at 540 nm. On equimolar basis, DHP had 40% of the reactivity of mimosine while
interference from other relevant compounds was 15–35%. The determination of mimosine and DHP in tissue samples under different
physiological conditions was effected after paper chromatographic separation of mimosine and DHP with distinctly differing
Rf, from other compounds. The indirect method is superior in terms of absolute selectivity, sensitivity and ease of applicability
with linear decreases in absorbance, proportional to increasing concentrations of mimosine from 0.1 to 0.75 μM or DHP from
0.2 to 1.5 μM and with recoveries of 99.2 to 100.5%. 相似文献
9.
Summary. The effect of different doses of cadmium and copper was studied in relation to growth and polyamine (Pas) metabolism in shoots
of sunflower plants. Cadmium accumulated to higher levels than copper and shoot length was reduced by 0.5 and 1 mM Cd, but
only by 1 mM Cu. At 1 mM of Cd or Cu, Put content increased 270% and 160% with Cd2+ and Cu2+, respectively. Spermidine (Spd) was modified only by 1 mM Cd, while spermine (Spm) declined after seeds germinated, increasing
thereafter but only with 1 mM Cd or Cu (273% over the controls for Cd and 230% for Cu at day 16). Both ADC and ODC activities
were increased by 1 mM Cd, whereas 1 mM Cu enhanced ADC activity, but reduced ODC activity at every concentration used. The
role of Pas as markers of Cd or Cu toxicity is discussed. 相似文献
10.
Summary. This study examined 10 wks of resistance training and the ingestion of supplemental protein and amino acids on muscle performance
and markers of muscle anabolism. Nineteen untrained males were randomly assigned to supplement groups containing either 20 g
protein (14 g whey and casein protein, 6 g free amino acids) or 20 g dextrose placebo ingested 1 h before and after exercise
for a total of 40 g/d. Participants exercised 4 times/wk using 3 sets of 6–8 repetitions at 85–90% of the one repetition maximum.
Data were analyzed with two-way ANOVA (p < 0.05). The protein supplement resulted in greater increases in total body mass, fat-free mass, thigh mass, muscle strength,
serum IGF-1, IGF-1 mRNA, MHC I and IIa expression, and myofibrillar protein. Ten-wks of resistance training with 20 g protein
and amino acids ingested 1 h before and after exercise is more effective than carbohydrate placebo in up-regulating markers
of muscle protein synthesis and anabolism along with subsequent improvements in muscle performance. 相似文献
11.
Summary. Taurine as well as tauret (retinyliden taurine) levels were measured in locust Locusta migratoria compound eyes. HPLC measurements revealed relatively low taurine levels (1.9 ± 0.16 mM) in dark-adapted eyes. Glutamate,
aspartate and glycine levels were 2.0 ± 0.2, 2.7 ± 0.4 and 3.0 ± 0.37 mM, respectively, while GABA was present only in trace
amounts. After about 4 h of light adaptation at 1500–2000 lx, amino acid levels in the compound eye were as follows: taurine,
1.8 ± 0.17 mM; glutamate, no change at 2.1 ± 0.2 mM; aspartate sharply increased to 4.7 ± 0.7 mM; glycine slightly decreased
to 2.8 ± 0.3 mM; and GABA trace levels. In the compound eye of locust Locusta migratoria, the existence of endogenous tauret in micro-molar range was established. In the dark, levels were several times higher compared
with compound eye after light adaptation 1500 lx for 3 h, as estimated by TLC in combination with spectral measurements. Existence
of tauret in compound eye is of special interest because in the compound eye, rhodopsin regeneration is based on photoregeneration. 相似文献
12.
Summary. Amino acids analysis in single wheat embryonic protoplast was performed using capillary electrophoresis equipped with laser-induced
fluorescence (CE-LIF), combination with tissue culture technique. Reagent fluorescein isothiocyanate (FITC) was introduced
into living protoplasts by electroporation for intracellular derivatization. A special osmotic buffer (0.6 mol/L mannitol,
5 mmol/L CaCl2) was used to keep the osmotic balance of embryonic protoplasts during the protoplasts derivatization. After completion of
the derivatization reaction in the protoplasts, a single protoplast was drawn into the capillary tip by electroosmotic flow.
Then a 0.1 M NaOH lysing solution was injected by diffusion. The derivatized amino acids were separated by capillary electrophoresis
and detected by laser-induced fluorescence detection after the protoplast was lysed Nine amino acids were quantitatively and
qualitatively determined and compared in lysate and single protoplast of wheat embryonic cells respectively, with mean concentrations
of amino acids ranging from 2.68×10−5 mol/L to 18.18×10−5 mol/L in single protoplast. 相似文献
13.
Summary. A randomised, double blind, placebo-controlled study was performed giving 0.5 g · kg−1 · day−1 of undiluted alanyl-glutamine (20%) or saline in a peripheral vein during 4 hours in ICU patients (n = 20). During the infusion
period a steady state in plasma concentration was reached for alanyl-glutamine, but not for alanine, glutamine or glutamate.
On the other hand there was no accumulation of any of the amino acids, as the pre-infusion concentrations were reached within
8 hours after the end of infusion. The half-life of the dipeptide was 0.26 hours (range, 0.15–0.63 h). The distribution volume
of alanyl-glutamine was larger than the extracellular water volume, indicating a rapid hydrolysis of the dipeptide. There
was no detectable alanyl-glutamine in the urine of any of the patients. All patients had excretion of small amounts of amino
acids in urine, but the renal clearance of alanine, glutamine and glutamate were not different between the two groups. 相似文献
14.
Summary. The purpose of this study was to determine whether the γ-aminobutyric acid (GABA) affects the rate of brain protein synthesis
in male rats. Two experiments were done on five or three groups of young rats (5 wk) given the diets containing 20% casein
administrated 0 mg, 25 mg, 50 mg, 100 mg or 200 mg/100 g body weight GABA dissolved in saline by oral gavage for 1 day (d)
(Experiment 1), and given the diets contained 0%, 0.25% or 0.5% GABA added to the 20% casein diet (Experiment 2) for 10 d.
The plasma concentration of growth hormone (GH) was the highest in rats administrated 50 mg and 100 mg/100 g body weight GABA.
The concentration of serum GABA increased significantly with the supplementation groups. The fractional (Ks) rates of protein
synthesis in brain regions, liver and gastrocnemius muscle increased significantly with the 20% casein + 0.25% GABA diet and
still more 20% casein + 0.5% GABA compared with the 20% casein diet. In brain regions, liver and gastrocnemius muscle, the
RNA activity [g protein synthesized/(g RNA·d)] significantly correlated with the fractional rate of protein synthesis. The
RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis in any organ. Our results
suggest that the treatment of GABA to young male rats are likely to increase the concentrations of plasma GH and the rate
of protein synthesis in the brain, and that RNA activity is at least partly related to the fractional rate of brain protein
synthesis. 相似文献
15.
High-efficiency induction of soybean hairy roots and propagation of the soybean cyst nematode 总被引:8,自引:0,他引:8
Cotyledon explants of 10 soybean [Glycine max (L.) Merr.] cultivars were inoculated with Agrobacterium rhizogenes strain K599 with and without binary vectors pBI121 or pBINm-gfp5-ER possessing both neomycin phosphotransferase II (nptII) and β-glucuronidase (gus) or nptII and green fluorescent protein (gfp) genes, respectively. Hairy roots were produced from the wounded surface of 54–95% of the cotyledon explants on MXB selective
medium containing 200 μg ml−1 kanamycin and 500 μg ml−1 carbenicillin. Putative individual transformed hairy roots were identified by cucumopine analysis and were screened for transgene
incorporation using polymerase chain reaction. All of the roots tested were found to be co-transformed with T-DNA from the
Ri-plasmid and the transgene from the binary vectors. Southern blot analysis confirmed the presence of the 35S-gfp5 gene in the plant genomes. Transgene expression was also confirmed by histochemical GUS assay and Western blot analysis for
the GFP. Attempts to induce shoot formation from the hairy roots failed. Infection of hairy roots of the soybean cyst nematode
(Heterodera glycines Ichinohe)-susceptible cultivar, Williams 82, with eggs of H. glycines race 1, resulted in the development of mature cysts about 4–5 weeks after inoculation. Thus the soybean cyst nematode could
complete its entire life cycle in transformed soybean hairy-root cultures expressing GFP. This system should be ideal for
testing genes that might impart resistance to soybean cyst nematode.
Received: 13 July 1999 / Accepted: 8 August 1999 相似文献
16.
Infiltrating detached maize (Zeamays L.) leaves with L-galactono-1,4-lactone (L-GAL) resulted in a 4-fold increase in the content of leaf ascorbate. Upon exposure to high irradiance (1000 μmol photons m−2 s−1) at 5 °C, L-GAL leaves de-epoxidized the xanthophyll-cycle pigments faster than the control leaves; the maximal ratio of de-epoxidized
xanthophyll-cycle pigments to the whole xanthophyll-cycle pool was the same in both leaf types. The elevated ascorbate content,
together with the faster violaxanthin de-epoxidation, did not affect the degree of photoinhibition and the kinetics of the
recovery from photoinhibition, assayed by monitoring the maximum quantum efficiency of photosystem II primary photochemistry
(Fv/Fm). Under the experimental conditions, the thermal energy dissipation seems to be zeaxanthin-independent since, in contrast
to the de-epoxidation, the decrease in the efficiency of excitation-energy capture by open photosystem II reaction centers (Fv′/Fm′) during the high-irradiance treatment at low temperature showed the same kinetic in both leaf types. This was also observed
for the recovery of the maximal fluorescence after stress. Furthermore, the elevated ascorbate content did not diminish the
degradation of pigments or α-tocopherol when leaves were exposed for up to 24 h to high irradiance at low temperature. Moreover,
a higher content of ascorbate appeared to increase the requirement for reduced glutathione.
Received: 20 May 1999 / Accepted: 29 October 1999 相似文献
17.
Kocsy G von Ballmoos P Suter M Rüegsegger A Galli U Szalai G Galiba G Brunold C 《Planta》2000,211(4):528-536
The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant
maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine (γEC) synthetase, the first enzyme
of GSH synthesis. At 25 °C, 1 mM BSO significantly increased cysteine and reduced GSH content and GSH reductase (GR: EC 1.6.4.2)
activity, but interestingly affected neither fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM
during chilling at 5 °C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost
40%. Buthionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition
of GSH or γEC together with BSO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels
of GSH and GR activity in roots and shoots. During chilling, the level of abscisic acid increased both in controls and BSO-treated
seedlings and decreased after chilling in roots and shoots of the controls and in the roots of BSO-treated seedlings, but
increased in their shoots. Taken together, our results show that BSO did not reduce chilling tolerance of the maize genotype
analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH, which also induced a decrease in
GR activity.
Received: 9 November 1999 / Accepted: 17 February 2000 相似文献
18.
The effect of extractants on degradation of L-glutamate and L-arginine in the course of shaking and filtration at low temperature 总被引:1,自引:0,他引:1
Summary. The effects of demineralized water (DEMI H2O) and 0.5 M ammonium acetate (0.5 M AAc) on losses of L-glutamic acid and L-arginine in the course of shaking and filtration
at low temperature (6 °C) were tested. The concentration of L-glutamic acid decreased by 6.3% in DEMI H2O and by 4.9% in 0.5 M AAc, whereas the L-arginine concentration decreased by 6.0% (DEMI H2O) and 10.7% (0.5 M AAc). We found a significantly (P < 0.05) higher degradation of L-arginine in 0.5 M AAc compared with that of DEMI H2O. 相似文献
19.
Atomic force microscopy (AFM) enables the topographical structure of cells and biological materials to be resolved under
natural (physiological) conditions, without fixation and dehydration artefacts associated with imaging methods in vacuo. It
also provides a means of measuring interaction forces and the mechanical properties of biomaterials. In the present study,
AFM has been applied for the first time to the study of the mechanical properties of a natural adhesive produced by a green
plant cell. Swimming spores of the green alga Enteromorpha linza (L.) J. Ag. (7–10 μm) secrete an adhesive glycoprotein which provides firm anchorage to the substratum. Imaging of the adhesive in its
hydrated state revealed a swollen gel-like pad, approximately 1 μm thick, surrounding the spore body. Force measurements revealed
that freshly released adhesive has an adhesion strength of 173 ± 1.7 mN m−1 (mean ± SE; n=90) with a maximum value for a single adhesion force curve of 458 mN m−1. The adhesive had a compressibility (equivalent to Young's modulus) of 0.54 × 106 ± 0.05 × 106 N m−2 (mean ± SE; n=30). Within minutes of release the adhesive underwent a progressive `curing' process with a 65% reduction in mean adhesive
strength within an hour of settlement, which was also reflected in a reduction in the average length of the adhesive polymer
strands (polymer extension) and a 10-fold increase in Young's modulus. Measurements on the spore surface itself revealed considerably
lower adhesion-strength values but higher polymer-extension values than the adhesive pad, which may reflect the deposition
of different polymers on this surface as a new cell wall is formed. The study demonstrates the value of AFM to the imaging
of plant cells in the absence of fixation and dehydration artefacts and to the characterisation of the mechanical properties
of plant glycoproteins that have potential utility as adhesives.
Received: 22 February 2000 / Accepted: 20 April 2000 相似文献
20.
Summary. The main objective of the present study was to evaluate the in vivo and in vitro effect of Arg on serum nucleotide hydrolysis. The action of Nω-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, on the effects produced by Arg was also examined.
Sixty-day-old rats were treated with a single or a triple (with an interval of 1 h between each injection) intraperitoneal
injection of saline (group I), Arg (0.8 g/kg) (group II), L-NAME (2.0 mg/kg or 20 mg/kg) (group III) or Arg (0.8 g/kg) plus
L-NAME (2.0 mg/kg or 20 mg/kg) (group IV) and were killed 1 h later. The present results show that a triple Arg administration
decreased ATP, ADP and AMP hydrolysis. Simultaneous injection of L-NAME (20 mg/kg) prevented such effects. Arg in vitro did not alter nucleotide hydrolysis. It is suggested that in vivo Arg administration reduces nucleotide hydrolysis in rat serum, probably through nitric oxide or/and peroxynitrite formation.
Both are first authors. 相似文献